android mesmerize (custom ringtones for text messages)

so everyone i have talked to, says it is not possible to set custom ringtones for your contacts when they text you, you can only have custom ringtones only for when they call... i hope thats not true, because i mostly text. but if someone could please find a way, or give me step by step directions on how to get- a custom ringtone for my contacts for when they text me, i will be very very thankful. if so, please write back on here- or email- di13anna@yahoo.com

i have us cellular. and i have the samsung mesmerize. in case u were wondering